1. Field of the Invention
This invention relates to a system for transferring very low temperature (cryogenic) liquid such as liquefied helium, liquefied nitrogen, and so forth from one container to another.
2. Discussion of Background
FIG. 5 of the accompanying drawing schematically illustrates a conventional very low temperature liquid transfer system as described, for example, in "MONOGRAPHS ON THE PHYSICS AND CHEMISTRY OF MATERIALS (Experimental Techniques in Low Temperature Physics, Storage and Transfer of Liquefied Gases, p.50, Oxford University Press, 1959)".
In the Drawing, a reference numeral 1 designates a very low temperature liquid such as liquefied helium, liquefied nitrogen, etc.; a numeral 2 refers to a first container to store therein the very low temperature liquid 1; a reference numeral 3 denotes a second container which is communicatively connected with the first container 2 through a connecting means 4 constituted by a transfer tube, and which stores therein the very low temperature liquid 1 to be transferred from the first container 2 by way of the transfer tube 4; a reference numeral 5 represents a liquid level sensor for measuring quantity of the very low temperature liquid 1 in the second container 3; and a reference numeral 6 designates a pressure control system which controls increase and decrease in the pressure within the first container 2 for the pressurized transfer of the very low temperature liquid 1 in the first container 2 to the second container 3 by way of the transfer tube 4, the pressure control system 6 in this drawing being constructed, as one example, with a pressurized gas source 7 for increasing pressure within the first container 2, a pressure reducing valve 8 for the pressurized gas, a pressure gauge 9 for detecting a pressure of the depressurized gas and a three-way electromagnetic valve 10 for increasing and decreasing pressure within the first container 2. A reference numeral 11 designates a control circuit which makes logical determination on an input signal from the liquid level sensor 5, and produces an output operating signal to the three-way electromagnetic valve 10, and a numeral 12 refers to a gas discharge port for discharging evaporated gas of the very low temperature liquid 1 in the second container 3 into the external atmosphere.
In the following, explanations will be given as to the operations of this very low temperature liquid transfer system. The quantity of the very low temperature (or cryogenic) liquid stored in the second container 3 is constantly monitored by the liquid level sensor 5 and the control circuit 11. When the quantity of the very low temperature liquid 1 in the second container 3 goes down below the lower limit value thereof, the liquid level sensor 5 denotes the quantity, and the control circuit 11 produces an output operating signal to start transfer of the liquid. With this operating signal, the three-way electromagnetic valve 10 begins to work, whereby the pressurized gas, which has come out of the pressurized gas source 7 and has been adjusted its pressure by means of the pressure-reducing valve 8 and the pressure gauge 9, is fed into the first container 2 by way of the three-way electromagnetic valve 10. By the pressure difference between the pressure in the first container 2 and the pressure in the second container 3, the very low temperature liquid 1 in the first container 2 is transferred into the second container 2 through the transfer tube 4. When the quantity of the very low temperature liquid 1 transferred into the second container 3 reaches the upper limit value thereof, the liquid level sensor 5 detects the liquid quantity and the control circuit 11 produces an output operating signal for stoppage of the liquid transfer. With this operating signal, the three-way electromagnetic valve 10 beings to operate to stop feeding of the pressurized gas from the pressurized gas source 7 into the first container 2, and, at the same time, to let the gas within the first container 2 out into the external atomosphere to offset a difference in pressure between the first container 2 and the second container 3, whereby the transfer of the very low temperature liquid 1 into the second container 3 is stopped. Incidentally, the discharge port 12 is provided in the second container 3, through which evaporated gas of the very low temperature liquid 1 is constantly discharged.
Since the conventional automatic transfer system of the very low temperature liquid is constructed as described above, it still requires monitoring by a human being outside the system, while it is being operated automatically, so as to prevent various abnormal situations from taking place, such as excessive rise in the pressure due to certain causes which are liable to bring about damage in the container; back-flow of evaporated gas in the second container 3 into the very low temperature liquid 1 within the first container 2 due to reversal of the pressure difference between the first container 2 and the second container 3; rise in the temperature within the second container 3 and increase in the evaporating speed of the very low temperature liquid in the second container 3 due to exhaustion of the very low temperature 1 in the first container 2 and direct feeding of the pressurized gas at a room temperature into the second container 3; and others